Fix LangVersion for C# projects

[stephentoub]

For some reason I've not yet determined, the Language==C# condition is failing, resulting in us using latest rather than preview for building all of our C# projects. Since all of our projects are C# except for a single VB project, I've just defaulted to preview unconditionally and overrode it in that single .vbproj (since VB doesn't allow "preview").

cc: @ViktorHofer

[ViktorHofer]

The msbuild <Language> property is defined in the language specific targets file, ie for C#: https://github.com/microsoft/msbuild/blob/3453beee039fb6f5ccc54ac783ebeced31fec472/src/Tasks/Microsoft.CSharp.CurrentVersion.targets#L39. This means that the property isn't available for comparison in Directory.Build.props. This was always broken and instead should have been placed in Directory.Build.targets.

[stephentoub]

This was always broken and instead should have been placed in Directory.Build.targets.

So the right fix is just to move the existing two lines into Directory.Build.targets instead?

[ViktorHofer]

Yes :)

[stephentoub]

I'll update it. But in the meantime, @ViktorHofer, what's going on here?

  Microsoft.DotNet.ToolPackage.ResolverCacheInconsistentException: more than one row for coverlet.console-1.7.0-net5.0-any-coverlet
     at Microsoft.DotNet.ToolPackage.LocalToolsResolverCache.TryGetMatchingRestoredCommand(RestoredCommandIdentifier restoredCommandIdentifier, CacheRow[] cacheTable, RestoredCommand& restoredCommandList)
     at Microsoft.DotNet.ToolPackage.LocalToolsResolverCache.TryLoad(RestoredCommandIdentifier restoredCommandIdentifier, RestoredCommand& restoredCommand)
     at Microsoft.DotNet.Tools.Tool.Restore.ToolRestoreCommand.PackageHasBeenRestored(ToolManifestPackage package, String targetFramework)
     at Microsoft.DotNet.Tools.Tool.Restore.ToolRestoreCommand.InstallPackages(ToolManifestPackage package, Nullable`1 configFile)
     at Microsoft.DotNet.Tools.Tool.Restore.ToolRestoreCommand.<>c__DisplayClass11_0.<Execute>b__0(ToolManifestPackage package)
     at System.Linq.Enumerable.SelectArrayIterator`2.MoveNext()
     at System.Linq.ParallelEnumerable.ToList[TSource](ParallelQuery`1 source)
     at System.Linq.ParallelEnumerable.ToArray[TSource](ParallelQuery`1 source)
     at Microsoft.DotNet.Tools.Tool.Restore.ToolRestoreCommand.Execute()
     at Microsoft.DotNet.Cli.DotNetTopLevelCommandBase.RunCommand(String[] args)
     at Microsoft.DotNet.Tools.Tool.ToolCommand.Run(String[] args)
     at Microsoft.DotNet.Cli.Program.ProcessArgs(String[] args, ITelemetry telemetryClient)
     at Microsoft.DotNet.Cli.Program.Main(String[] args)

[ViktorHofer]

#33837. I'm working on a fix (workaround) right now.

[stephentoub]

As a benefit of that error / callstack, I noticed dotnet/sdk#10937 😄

[ViktorHofer]

Nice!

[stephentoub]

@ViktorHofer, I'm undoing your suggested change; it breaks everything 😦

[ViktorHofer]

OK sorry :(

[stephentoub]

No worries :)